The overall objective of this project is to utilize cardiac cells grown in vitro as a model for studying anthracycline-induced cardiotoxicity in treated cancer patients. Methodologies have been developed for the establishment of heart cell cultures from neonatal rats such that the function (beating capability) of these non-dividing cell populations can be utilized as an indicator of their viability or physiological capacities. A computerized system of analysis has been developed to measure the interval of time between contractions of single or groups of synchronously beating cells at the millisecond level. A microscopic stage has been designed here to accurately control temperature and pH, two variables to which cardiac cells are particularly sensitive. A variety of techniques will be utilized to study the mechanisms of toxicity of Adriamycin, Adriamycin analogues (AD 32) and other anti-cancer agents on the function and viability of these post-mitotic cells. These will include: light and electron microscopy, to assess structural damage; assays of beta-galactosidase, an enzyme found in high amounts in heart muscle cells; RNA and DNA assays, to evaluate synthesis and repair; and metabolic inhibitors, as probes for distinguishing between glycolytic and electron transort effects. A clinical relevance for this in vitro approach has already been demonstrated here with two preliminary observations: 1) a direct effect, both nucleolar and mitochondrial, in cardiac cells treated with Adriamycin in culture; and 2) Adriamycin-induced arrhythmias which are dose dependent and are distinct from structural damage at early times.